1. Field of the Invention
This invention relates to a broad band switching system for the selective connection of broad band signal sources to subscribers receiving broad band signals by way of a broad band switching network in which the cross point circuits, whose function is to selectively connect input lines to output lines of the switching network in view of signals to be through-connected, the signals having signal frequencies of, for example, up to more than 100 MHz and being angle modulated with broad band signals, can be formed by means of linkage elements realized in emitter-coupled logic (ECL) technology.
2. Description of the Prior Art
The ECL technology mentioned above is disclosed in German allowed and published application 2,828,662 and is generally set forth in Pfannschmidt: "Arbeitsgeschwindigkeitsgrenzen von Koppelnetzwerken fur Breitband-Digitalsignale", Dissertation, Technical University Braunschweig, 1978.
Given a broad band switching network of the type generally set forth above, television programs can be switched, for example, to subscribers who wish to receive the same, as is involved in recent developments of telecommunications which lead to broad band communication networks having subscriber lines formed with light wave guides, whereby a star network of light wave guides having one light wave guide per dwelling unit proves favorable at the subscriber level, the light wave guide connecting a broad band switching location (advantageously spatially united with the nearest telephone switching location) to the dwelling of the subscriber and by way of which all telecommunication services for the appertaining dwelling unit are sequenced, whereby offering, for example, at least approximately the following communication possibilities comes into consideration for a dwelling unit, which does justice to future developments:
three video channels for three video receivers having independent access to all television signal sources which can be reached by the switching location or, respectively, television programs which are available in the switching location; and three return channels for program selection and, under certain conditions, for sequencing interactive services, as well as a greater number of very high frequency (VHF) radio channels (stereo,
NTZ 32 (1979) 3, pp. 150-153 and Antennen Information No. 63, June 1979, pp. 3-5.
In such TV program switching, it does not suffice that a multitude of subscriber terminals can be simultaneously connected to one and the same program source but, rather, vice-versa, one and the same subscriber terminal must also be able to simultaneously be connected to a plurality of program sources. To this end, it is known to provide subscriber-specific frequency multiplexers at the broad band switching center and to provide a frequency demultiplexer at each subscriber and to transmit the greatest programs in frequency division multiplex by way of a light wave guide. (Antennen Information No. 63, June 1979, pp. 3-5). This requires a corresponding multiplex expense and the present invention provides a technique for reducing such expense.